(1) Field of the Invention
The present invention relates to a bandpass filter, and more particularly to a bandpass filter suitable for use in a frequency range including and above the UHF band.
(2) Description of the Prior Art
A bandpass filter for use in the frequency range noted above is required to have a very high degree of Q factor for its filter characteristics. Existing filters include a stripline filter as disclosed in U.S. Pat. No. 4,157,517, and filters as disclosed in Japanese Utility Model Publication No. 53-40121 and Utility Model Laying-Open Publication No. 56-78572 wherein conducting layers are formed on a substrate.
In the case of the stripline filter, an electrode must be formed over an entire back face area of the substrate. This necessitates a large amount of electrode material, which results in high cost of the filter. In the case of the filter having conducting layers formed on the substrate, a plurality of resonators each including one inductance element and one capacitance element connected in parallel are coupled to one another by coupling means such as capacitance elements. Such a construction requires the coupling elements in addition to the resonators, and therefore is large in size and troublesome to assemble.